Fluorescent lighting



S 1945- R. w. KEISER ET AL.

FLUORESCENT LIGHTING Filed June 1, 1943 2O wmemmmk 9 msc A s 5 mw r a .5 W?

r M .5 if 7 5 i 5 6 U1?! 4. m 6 T 5 Patented Aug. 14, 1945 FLUORESCENT LIGHTING Russell W. Keiser and Charles P. Boucher, At-

lanta, 6a., assignors to Boucher and Keiser Company, Atlanta, Ga., a partnership composed of Charles P. Boucher and Russell W.

Keiser Application June 1, 1943, Serial No. 489,304

4 Claims.

This invention relates to fluorescent lighting and particularly to transformer for supplying current to fluorescent lamps.

It is a general object of the present invention to provide a novel and improved transformer for supplying current from a power source to a pair of fluorescent lamps.

More particularly it is an object of the invention to provide such a. transformer using a minimum of iron and copper while providing maximum operating efliciency and light intensity with a minimum of heating.

An important feature of the invention consists in the construction of a transformer of the type adapted to be interposed between a source of alternating current and a pair of fluorescent lamps which can be so operated as to eliminate stroboscopic effects and wherein the wave form of the current supplied to the two lamps is such as to provide maximum illumination therefrom equalized between the lamps.

A further feature of the invention resides in the construction of a transformer wherein the primary winding and the two secondary windings are sequentially arranged on a core providing a closed magnetic circuit and in which magnetic shunts'are provided for effecting such leakage fluxes a to provide high inherent reactance to insure uniform distribution of current both to the lamp receiving leading current and to that operated by lagging current.

The invention incorporates in addition to the transformer function, means for providing current at the proper voltages to each of two lamps and means for restricting the current to each of the lamps, which have a negative resistance, so that it is limited to the proper operating values for the same under all conditions.

Other and further objects and features of the invention will be more apparent to those skilled in the art on consideration of the accompanying drawing and the following specification wherein are disclosed several exemplary embodiments of the invention and the understanding that such modifications may be made therein such as fall within the scope of the appended claims without departing from the spirit of the invention.

In said drawing:

Fig. 1 is a schematic wiring drawing showing a pair of fluorescent lamps connected with a power circuit through a transformer constructed in accordance with the present invention;

Fig. 2 is a plan view of the assembled transformer;

Fig. 3 is an end view of the same;

Fig. 4 is a plan view of the core assembly without the several windings; and

Fig. 5 illustrates a modified form of core structure.

In the operation of fluorescent lamps it is necessary to provide some means for the delivery of proper voltage and current from a power source to the lamps. Lamps of various sizes are made and used and each requires a different o rating voltage. These voltages are not the same, in any case, as the normal sources of commercial power, and furthermore the construction of the lamps is such that they have a negative resistance, 1. e., the current flow would continue to increase until the lamp was destroyed if means were not provided to limit the same. Where lamps are intended to be used, without transformers, in connection with commercial power sources either a resistance or an inductance is necessary to limit the current. Both of these devices are relatively uneconomical because of the heat losses therein.

The over-all voltage necessary to supply both the lamp and its reactance is usually greater than that available from commercial sources of supply and it is almost the universal practice to use a transformer to obtain the proper voltage. In accordance with the present invention it is proposed to combine the functions of the transformer and the reactance. It is preferred to operate two lamps simultaneously, one excited by a leading current and the other by a lagging current so as to eliminate stroboscopic effects and the slight flickering which is annoying to some people, and for this purpose a double secondary is provided on the transformer. preferred is one adapted to supply a substantially constant current and for this purpose is constructed to have high leakage reactances. Advantage is taken of these leakage reactances for obtaining a. proper distribution of current in the two secondaries and to insure a desirable wave form whereby both lamps are lighted to maximum brilliance with uniform distribution of light between the same.

'In construction of the transformer every effort has been made to provide a design giving maximum economy of critical materials such as copper.and steel without impairing the efficiencies which have been established as desirable in the operation of hot cathode starting fluorescent lamps. The design provides for an assembly which requires a minimum of labor and which operates on the autotransformer principle to reduce the number of turns of wire.

Referring now to the circuit diagram of Fig. 1

The type of transformer for a better understanding of the invention, it will be seen that the two lamps ill and I2 are of conventional form, each provided with two end-filaments to establish hot cathode starting. A source of alternating current power is shown at l4, connected to the terminals of a primary winding it. of an autotransformer, assembled on a core Hi. In addition the core contains two secondar windings I! and 20. One end of each of these windings is connected throu h c nductor 2| to terminal 22 of the primary. The winding it has its opposite end connected to a condenser 25 whose purpose it is to cause the current delivered by this windin to lead the voltage therein. From the condenser 25 a conductor connects to the compensator 26 conventional form used for the purpose of providing the necessary induction kick in the circuit of the leading lamp to improve the speed of ignition. Conductor 21 leads from the compensator to one terminal of the right-hand filament f l mp I 2. The free end of secondary 20 leads by conductor 28 to one end of the left-hand filament of lamp I0. One terminal of each of the opposite ends of the two lamps is connected throu h a conductor 28 to terminal 30 of the primary. The remaining terminals of the filaments in each lamp are adapted to be connected together through starting switches an or 3|, of any desired or conventional form, in well known manner.

It will be seen that the connect ons .iust described provide autotransformer o erat on for the two lamps wherein the two secondaries need provide only that voltage necessary above that of the source l4 for the operation of their respective lamps.

The transformer secondaries not only provide the necessary potential for actuating the two lamps but they also act to limit the current because of the high leakage reactance provided in the core structure which will be subsequently de scribed.

Referring now to Fig. 2 for the physical arrangements of the elements of the transformer it will be seen that the core structure is more or less conventional, including a central or winding leg 3!, a pair of end members 38 and 31 and a pair of closing legs 38 and 38. These latter are duplicates and if desired one can be eliminated for simplification. However, the closing legs are shown as having only half the cross-section of that of the winding leg so that combined they provide paths of adequate cross-section for the magnetic flux without becoming saturated. In fact one of the features of the present transformer is the workin of the core at low-saturation levels to maintain a good wave-form for the current to obtain maximum illumination from the lamps.

On the core are shown the three windings l5, l8 and 20 sequentially arranged, with the primary l tightly against the and member 31 and the lagging secondary 20 tightly against end member I. Relatively wide spacing is shown between the two secondaries and between the primary and the secondary which delivers leading current. In these spaces magnetic shunts are provided as shown. The magnetic shunts between the primary and the leading secondary are designated as 40 and are duplicated on the two sides of the winding leg and extend substantially to the closing legs, leaving small air gaps 4|. The magnetic shunts between the two secondary windings are designated 42, are disposed in the same manner as the shunts 4|) and provided with similar air gaps 44. It will be noted, however. that the crosssectional area of the magnetic shunts 42 is slightly more than twice that of the shunts 4|.

As seen in Fig. 4 the core may conveniently be formed by a stack of laminations each including an E-shaped punching 45 and a single end member 45, the E-shaped punching including the two closing legs 38 and 39, the winding leg 35 and one of the end members 35. The other end member is merely a straight rectangular piece closing the E and permitting assembly of the windings. As shown by the dotted lines 41 it is preferred to alternate the Es and the closing plates to stagger the air gaps in alternate laminations. In this construction as well as in that of Fig. 2 the shunts are composed of a plurality of laminations oi the same thickness and type of metal as the main ones but arranged in planes at right angles to those of the main laminaticns. For convenience in assembling, these are bunched together and taped and can be positioned alter the windings are in place. The several air gaps are maintaine by inserting insulating strips 50 of appropriate thickness which also serve to wedge the shunts in position. Following more or less standard practice the core and the assembled coils are appropriately impregnated with varnish Or like insulating material and baked which serves to hold all the parts tightly together to prevent any humming. The insulation of the whole assembly is also improved.

In Fig. 5 is shown an alternativ form of core structure equally as effective but using more material than that shown in Fig. 4 where it may be noted that the closing strips 46 can be punched from between the parts of the Es and also that sufilcient metal may be obtained in punching these main laminations to provide the strips for the shunts. In this manner there is no wastage of metal whatsoever. In Fig. 5 the central leg 35' is made up of a stack 01' rectangular larnlnations on which the windings can be assembled in appropriate spaced relation. The two side members 55 and 55', identical in construction, include the closing legs of the core and portions of the end members as well as the integral shunts 56 and 51. These shunts are of such length that air gaps are formed at the winding leg as shown at 58. These laminations may be assembled in stacks and combined with the wound core 35' into a complete transformer held together by assemblage in a casing which can be poured full of pitch or similar material to prevent vibration. This form of core structure is simpler to assemble and while using more material does provide for less labor..

It will be appreciated that extra voltage is necessary to actuate lamp I! over that necessary for lamp l0 because of the voltage drops which will occur in the condenser 25 and in the compensator 26. For this reason, winding l8 contains more turns than winding 20. In the circuit as shown, however, the actual potential applied across the terminals of the two lamps will be substantially identical.

In order to provide the necessary reactance in the two secondary windings to limit the currents to the proper amount of each lamp, high leakage reactances are effected by the use of such shunts in the magnetic circuit as have just been described. The position of the primary winding in respect to the two secondaries is of extreme importance in assuring uniform operation of the twolamps and in the obtaining of a satisfactory wave form for the current to both of them. A central position of the primary has proven entirely unsatisfactory, because under this condition the primary flux interfered greatly with the wave form of the current to the leading lamp. The wave form of the current supplied to the leading lamp is further improved by the presence of the starting compensator 26 in the circuit supplying the lamp from the secondary winding l8.

The specific arrangement of the primary and two secondary windings on the transformer core and the positioning and relative sizes of the magnetic shunts has been carefully selected to achieve maximum eificiency with minimum use of core material and wire. Every eilort has been made to eliminate unfavorable reactions from the primary leakage and counter-E. M. F. fluxes on the wave form of the currents flowing in the secondary circuits. The high inherent leakage reactance of the primary winding aided by the magnetic shunts 40 and their small air gaps materially curtails any tendency toward reaction between the primary and the several secondaries. The large magnetic shunts existing between the two secondaries curtail interaction between them to the necessary extent without preventing that necessary interchange of power between the lead and lag lamps at the time of starting in the event that one or the other starts first.

To fully appreciate the advantages of the present unit the following dimensions and characteristics of a successful example may be noted. The unit was constructed for operation with a pair of the popular 40 watt size fluorescent lamps. The iron core operates at the relatively low flux density of 11,600 gausses. Each of the windings consists of #26 copper wire, the primary having 710 turns, the leading secondary 649 turns and the lagging secondary 601 turns making a total of 1960. The total iron in the core is just a fraction less than 3.8 lbs.

On test the unit gave the following results: Primary input 118 volts-primary current .855 ampere-lead lamp current .410 ampere-lead lamp operating volts 11l-lag lamp current .425 ampere-lag lamp volts 109. These conditions exist with both lamps operating.

With lag lamp only lighted-primary current input .525 ampere-voltage across lead lamp sockets 177-lag lamp current .290-lag lamp voltage 14.

With lead lamp only lighted-primary current .572 ampere-lead lamp current .530 amperelead lamp operating volts 97-voltage across lag lamp sockets 234.

Both lamps started from a cold condition in less than 5 seconds. With the whole unit hot. starting requires less than seconds. In comparison with the best of the available operating units on the market, the present device eflects a saving of 21.6% copper and 23.6% core material without any reduction in efliciency, wave form or light intensity.

It will be appreciated that the above figures are only illustrative and that the unit can be made in any desired or required size for handling two lamps of any wattage. Likewise it can be arranged so that a plurality of lamps in parallel can be operated from both the leading and the lagging secondary.

What we claim is:

1. In a transformerfor connection between a source of alternating current and a pair of fluorescent lamps, in combination, a core structure providing a, closed magneticpath, a primary winding, a leading current secondary winding and a lagging current secondary winding, said three windings being sequentially arranged on said core, said core having a shunt positioned between the primary and leading current secondary to provide high primary leakage flux and a second shunt positioned between the secondary windings to provide high leakage flux for both secondary windings, the second of said shunts having a cross-section of the order of twice that of the first.

2. In a transformer for connection between a source of alternating current and a pair of fluorescent lamps, in combination, a core structure providing a closed magnetic path, a primary winding, a leading current secondary winding and a lagging current secondary winding, said three windings being sequentially arranged on said core, said core having a shunt positioned between the primary and leading current secondary to provide high primary leakage flux and a second shunt positioned between the secondary windings to provide high leakage flux for both secondary windings, the second of said shunts having a cross-section of the order of twice that of the first and each of said shunts having an air gap of the same length.

3. In a transformer for connection between a source of alternating current and a pair of fluorescent lamps, in combination, a core structure of rectangular configuration including a winding leg, end members and a closing leg, a primary winding on the winding leg close against one of the end members, a lagging current secondary on the same core leg and against the other end member, a leading current secondary on said core leg and positioned between and spaced from the other windings, a magnetic shunt between the primary and leading secondary coils and extending between the core legs, a second magnetic shunt between the two secondary coils extending between the core legs having a cross-section substantially twice that of the first shunt.

4. In a transformer for connection between a source of alternating current and a pair of fluorescent lamps, in combination, a core structure of rectangular configuration including a winding leg, and members and a closing leg, 9. primary winding on the winding leg close against one of the end members, a lagging current secondary on the same core leg and against the other end member, a leading current secondary on said core leg and positioned between and spaced from the other windings, a magnetic shunt between the primary and leading secondary coils and extending between the core legs, a second magnetic shunt between the two secondary coils and extending between the core legs. each of said shunts having an air gap therein and said second mentioned shunt having a cross-section of the order of twice that of the first.

RUSSELL W. KEISER.

CHARLES P. BOUCHER 

